bonding grounding and earthing
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What is the difference between Bonding, Grounding and Earthing?
What is the difference between Bonding,Grounding and Earthing?
Content
1. Introduction2. Bonding
3. Earthing
4. Grounding
5. Micro Difference between Earthing and Grounding
6. Illegal Practice of interchange Purpose of Grounding and earthing wire
7. Conclusion
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The earthing connection to switchboard rear door
(metal parts)
Introduction
One of the most misunderstood and confused concept is difference between Bonding, Grounding
and Earthing. Bonding is more clear word compare to Grounding and Earthing, but there is a micro
difference between Grounding and Earhing.
Earthing and Grounding are actually different terms for expressing the same concept.
Ground or earth in a mains electrical wiring system is a conductor that provides a low impedance pathto the earth to prevent hazardous voltages from appearing on equipment. Earthing is more commonly
used in Britain, European and most of the commonwealth countries standards ( IEC, IS), while
Grounding is the word used in North American standards (NEC, IEEE, ANSI, UL).
We understand that Earthing and Grounding are
necessary and have an idea how to do it but we
dont have crystal clear concept for that. We need to
understand that there are really two separate things
we are doing for same purpose that we call
Grounding or Earthing. The Earthing is to reference
our electrical source to earth (usually via
connection to some kind of rod driven into the
earth or some other metal that has direct contact
with the earth).
The grounded circuits of machines need to have an
effective return path from the machines to the power
source in order to function properly (Here by
Neutral Circuit).
In addition, non-current-carrying metallic
components in a System, such as equipment
cabinets, enclosures, and structural steel, need to
be electrically interconnected and earthed properly
so voltage potential cannot exist between them. However, troubles can arise when terms like
bonding, grounding, and earthing are interchanged or confused in certain situations.
In TN Type Power Distribution System, in US NEC (and possibly other) usage: Equipment is
earthed to pass fault Current and to trip the protective device without electrifying the device enclosure.Neutral is the current return path for phase. These Earthing conductor and Neutral conductor are
connected together and earthed at the distribution panel and also at the street, but the intent is that no
current flow on earthed ground, except during momentary fault conditions.
Here we may say that Earthing and grounding are nearly same by practice.
But In the TT Type Power Distribution System (in India) Neutral is only earthed (here it is actually
called Grounding) at distribution source (at distribution transformer) and Four wires (Neutral and
Three Phase) are distributed to consumer. While at consumer side all electrical equipment body are
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connected and earthed at consumer premises (here it is called Earthing).
Consumerhas no any permission to mix Neutral with earth at his premises here earthing and
grounding is the different by practice.
In both above case Earthing and Grounding are used for the same Purpose. Lets try to understand
this terminology one by one.
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Bonding
Bonding is simply the act of joining two electrical conductors together. These may be two wires, a
wire and a pipe, or these may be two Equipments. Bonding has to be done by connecting of all the
metal parts that are not supposed to be carrying current during normal operations to bringing them to
the same electrical potential.
Bonding ensures that these two things which are bonded will be at the same electrical potential. That
means we would not get electricity building up in one equipment or between two different equipment.
No current flow can take place between two bonded bodies because they have the same potential.
Bonding itself, does not protect anything. However, if one of those boxes is earthed there can be
no electrical energy build-up. If the grounded box is bonded to the other box, the other box is also at
zero electrical potential.
It protects equipment and person by reducing current flow between pieces of equipment at different
potentials.
Theprimary reason for bonding is personnel safety, so someone touching two pieces of equipment a
the same time does not receive a shock by becoming the path of equalization if they happen to be at
different potentials. The Second reason has to do with what happens if Phase conductor may be
touched an external metal part.
The bonding helps to create a low impedance path back to the source. This will force a large current to
flow, which in turn will cause the breaker to trip.
In other words, bonding is there to allow a breaker to trip and thereby to terminate a fault.
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Typical bonding connection
Bonding to electrical earth is used extensively to ensure that all conductors (person, surface and
product) are at the same electrical potential. When all conductors are at the same potential no
discharge can occur.
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Earthing
Earthing means connecting the dead part(it means the part which does not carries current under
normal condition) to the earth for example electrical equipments frames, enclosures, supports etc.
The purpose of earthing is to minimize the risk of receiving an electric shockif touching metal parts
when a fault is present. Generally green wire is used for this as a nomenclature.
Underfault conditions the non-current carrying metal parts of an electrical installation such as frames,
enclosures, supports, fencing etc. may attain high potential with respect to ground so that any person or
stray animal touching these or approaching these will be subjected to potential difference which may
result in the flow of a current through the body of the person or the animal of such a value as may prove
fatal.
To avoid this non-current carrying metal parts of the electrical system are connected to the general
mass of earth by means of an earthing system comprising of earth conductors to conduct the fault
currents safely to the ground.
Earthing has been accomplished through bonding of a metallic system to earth. It is normally achieved
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by inserting ground rods or other electrodes deep inside earth.
Earthing is to ensure safety or Protection of electrical equipment and Human by discharging
the electrical energy to the earth.
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Grounding
Grounding means connecting the live part(it means the part which carries current under normal
condition) to the earth for example neutral of power transformer. It is done for the protections of power
system equipment and to provide an effective return path from the machine to the power source.
For example grounding of neutral point of a star connected transformer.
Grounding refers the current carrying part of the system such as neutral (of the transformer or
generator).
Because of lightening, line surges or unintentional contact with other high voltage lines, dangerously
high voltages can develop in the electrical distribution system wires. Grounding provides a safe,
alternate path around the electrical system of your house thus minimizing damage from such
occurrences.
Generally Black wire is used for this as a nomenclature.
All electrical/electronic circuits (AC & DC) need a reference potential (zero volts) which is called ground
in order to make possible the current flow from generator to load. Ground is May or May not beearthed. In Electrical Power distribution it is either earthed at distribution Point or at Consumer end but
it is not earthed in Automobile( for instance all vehicles electrical circuits have ground connected to the
chassis and metallic body that are insulated from earth through tires).
There may exist a neutral to ground voltage due to voltage drop in the wiring, thus neutral does not
necessarily have to be at ground potential.
Cant see this video? Clickhere to watch it on Youtube.
In a properly balanced system, the phase currents balance each other, so that the total neutral current is
also zero. For individual systems, this is not completely possible, but we strive to come close in
aggregate.
This balancing allows maximum efficiency of the distribution transformers secondary winding.
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Micro Difference between earthing and Grounding
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There is no major difference between earthing and Grounding, both means Connecting an electrical
circuit or device to the Earth. This serves various purposes like to drain away unwanted currents, to
provide a reference voltage for circuits needing one, to lead lightning away from delicate equipment.
Even though there is a micro difference between grounding and earthing:
1. Difference in Terminology
In USA term Groundingis used but in UK term Earthingis used.
2. Balancing the Load Vs Safety
Ground is a source for unwanted currents and also as a return path for main current some times.
While earthing is done not for return path but only for protection of delicate equipments. It is an alternate
low resistance path for current.
When we take out the neutral for a three phase unbalanced connection and send it to ground, it is
called grounding. Grounding is done to balance unbalanced load. While earthing is used between the
equipment and earth pit so as to avoid electrical shock and equipment damage.
3. Equipment Protection Vs Human Safety
Earthing is to protect the circuit elements whenever high voltage is passed by thunders or by any othersources while Grounding is the common point in the circuit to maintain the voltage levels.
Earth is used for the safety of the human body in fault conditions while Grounding (As neutral
earth) is used for theprotection of equipment. Earthing is a preventive measure while Grounding is
ust a return path.
The ground conductor provides a return path for fault current when a phase conductor accidentally
comes in contact with a grounded object. This is a safety feature of the wiring system and we would
never expect to see grounding conductor current flow during normal operation.
IMPORTANT:Do not Ground the neutral second time when It is grounded either at
Distribution Transformer or at Main service panel of Consumer end.Grounding act as neutral.
But neutral cannot act as ground.
4. System Zero Potential Vs Circuit Zero Potential
Earthing and Grounding both is refer to zero potential, but the system connected to zero potential is
differ than Equipment connected to zero potential .If a neutral point of a generator or transformer is
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connected to zero potential then it is known as grounding.
At the same time if the body of the transformer or generator is connected to zero potential then it is
known as earthing.
The term Earthing means that the circuit is physically connected to the ground and it is Zero Volt
Potential to the Ground (Earth) but in case of Grounding the circuit is not physically connected to
ground, but its potential is zero(where the currents are algebraically zero) with respect to other point,
which is also known as Virtual Grounding.
Earth having zero potential whereas neutralmay have some potential. That means neutral does not
always have zero potential with respect to ground. In earthing we have Zero Volt potential references to
the earth while in grounding we have local Zero Volt potential reference to circuit. When we connect
two different Power circuits in power distribution system, we want to have the same Zero Volt reference
so we connect them and grounds together.
This common reference might be different from the earth potential.
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Illegal Practice of interchange Purpose of Grounding andearthing wire
Neutral wire in grid connections is mandatory for safety. Imagine a person from 4th floor in a building
uses Earth wire (which is earthedin the basement at Basement) as neutral to power his lights.
Another Person from 2nd floor has a normal setup and uses neutral for the same purpose. Neutral wire
is also earthed at the ground level (as per USA practice Neutral is Grounded (earthed) at Building
and as per Indian Practice it is Grounded (earthed) at Distribution Transformer).
However, ground wire (Neutral wire) has a much lower electrical resistance than Earth Wire
(Earthing) which results in a difference of electrical potential (i.e. voltage) between them. This voltage
is quite a hazard for anyone touching a Earth wire (Metal Body of Equipment) as it may have several
tens of volts.
The second issue is legality. Using ground wire instead of neutral makes you an energy thief as the
meter uses only the Phase and neutral for recording your energy consumption. Many Consumers make
energy theft by using Earthing wire as a Neutral wire in an Energy meter.
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Conclusion
Ground is a source for unwanted currents and also as a return path for main current. While earthing is
done not for return path but only for protection of delicate equipments. It is an alternate low resistance
path for current.
Earth is used for the safety of the human body in fault conditions while Grounding (As neutral earth) is
used for the protection of equipment.
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